I usually go by 1/2 retail as a fair price to pay for something that is in 7 out of 10 condition. So at roughly $600 - $700 new I would expect to pay $300-$350 used. Where it gets tricky is end of life products that are discontinued or no longer made. While 1/2 price is still fair if it is in really good condition, products old enough to actually be out of production are worth generally between 30% and 50% of retail. Obviously a product that was continued a few month ago such as the K10 can still be found new in stores even though it is technically discontinued. So it will still demand a fair rate. While a product that has been out of production for several years may not demand nearly as high as its condition may wishfully like.
For example. I have a couple of EAW LA212's up for sale currently. They still sell for about $1,000 new in stores that have them in stock. EAW discontinued them last year if I am not mistaken? You can still find them new, but the used prices has plummeted and now you can get them for around $350 used...... Not cool if you're me. Are they worth more? Yes, but only to those willing to spend the money on something that can't be readily replaced. So this means people are not going to spend as much on something that can't be easily replaced. I.E. used K10's are on borrowed time before the price plummets. The fact that there is a K10.2 helps maintain some value because they look the same, but as soon as big name stores show discontinued, or no longer in stock, the price will hit a floor.
What do I think the K10's are worth? I think that $350 is a really good price and if you can get them for less then jump for joy. I do not see them being worth much more than $400 on even a good day. I wouldn't cry too much about $400 if that is all you can walk him down to, but keep in mind that 6 months to a year from now they will be worth less than $350 for sure..... no matter how good the condition they are in.
